Wow -- it has actually been 20 years since Myst came out?? That seems unbelievable. I haven't done any "real" computer gaming in a long time, but I spent many hours working my way through Myst and absolutely loved that game.
I wonder if the popularization of the World Wide Web had something to do with the eventual decline of Myst and games like it. I remember that a big part of the satisfaction of playing Myst and other puzzle-based games, such as the King's Quest series, was that you really needed to struggle through the challenges until you figured them out. For example, a staple of those games was a maze that you had to traverse at some point (remember the little subterranean train thing in Myst?). To solve them, you had to spend considerable time exploring and mapping until you finally figured out how to get where you needed to go. If you were stuck, there wasn't much you could do except try harder until you got it. Sure, the game companies had "hot lines" that you could call for hints, but they charged you for it, and nobody I knew ever used them. As a result, the game was much more rewarding because you had to do it all by yourself. This environment also was conducive to playing the game with others, because two (or more) heads are better than one. My brother and I worked through a number of these games when we were kids, and playing them together added to the fun.
Once the Web became mainstream, the situation changed very quickly. Suddenly, game "walk throughs" were widely available for free, and much of the mystique that led to these games' success disappeared. You need to solve that maze? Just look it up on the walk through and you can be done with it in about two minutes. Once the entire game solution was readily available, the sense of accomplishment from solving the puzzles was greatly diminished, in my opinion.
So, imagine a world where there is no quick, easy way to look up game solutions. It seems terribly quaint now, but that was the environment in which Myst and similar games before it became popular. Once that changed, I think the days were numbered for the puzzle-based games, at least as far as their ability to become blockbusters.
I haven't done any research to compare how well actual market trends correlated with the rise of the Web. This is just my recollection of how the gaming world changed during that time.